Studies of powdered fertilizers or nutrients have shown them to be effective fertilizers, being essentially equivalent to granular applications. However, the practical considerations of applying powdered products on a field scale meant that these products have not been available to farmers and producers. For example, most oxide products come in high analysis (60-80 percent actual metal) while most micronutrients are applied in low units per land measure (e.g. 1-10 pounds actual per acre). Furthermore, many micronutrient products are applied in heterogeneous blends with other fertilizers (nitrogen phosphate etc.) These products and/or blends typically have densities in the 45-65 lb per cubic foot range. Existing micronutrient products are typically in the 95+ density range meaning that the blend does not hold its integrity during extended storage as is common in agriculture or if the product is transported over rough terrain. In addition, the higher density means that the nutrients are not spread evenly on the field.
Past work with powdered nutrients by the inventors has shown that it is possible to coat macro fertilizer with 0.1 to 2 percent weight to weight of powdered nutrients directly onto dry macro fertilizers such as urea, phosphate granules, potash granules and the like, without the use of binders, as discussed in U.S. Pat. No. 7,445,657. However, in some cases it can be difficult to obtain a coating above 1 percent (w/w) on certain carriers, for example, if the prills or granules have a substantially smooth surface or are larger than average. Furthermore, as discussed below, using this method, it is often only possible to coat the outer surface of the carrier with a single layer of the powder.